Even though the roof was closed at Lucas Oil Stadium, it was a day of thunderbolts — thunderbolts delivered by the underdog Rams.

Chris Long’s first NFL touchdown. Tavon Austin scoring touchdowns without having them called back by penalty. You talk about strange sights at Lucas Oil. The Rams had four touchdowns of 45 yards or more, building up a lead that not even phenom Indianapolis quarterback Andrew Luck could overcome.

The 38-8 Rams triumph Sunday was their largest victory since a 48-17 thrashing of Minnesota in 2003 — the Rams’ last division championship year.

En route to a 28-0 halftime lead, defensive end Robert Quinn got the Rams’ party going with a strip sack of Luck on the opening series of the game. Long scooped up the fumble and raced 57 yards for a score just 2 minutes 48 into the contest. Quinn’s gave him 11 for the season and a career high.

Late in the first quarter, the Rams missed an opportunity to make it 14-0 when a bad exchange between quarterback Kellen Clemens and running back Zac Stacy resulted in a fumble in the backfield on third-and-goal from the Indy 5. Cassius Vaughn recovered at the 8 for the Colts.

But on this day it didn’t matter; that red zone turnover was a mere speed bump for the Rams, who raced to a 28-0 halftime lead and were up 38-zip before the Colts got on the scoreboard.

Late in the first quarter, an 18-yard punt return by Austin gave the Rams the short field with the offense taking over at the Indianapolis 43. On third-and-3 from the Indianapolis 36, Clemens rolled out and connected on a short pass to Chris Givens who turned upfield and nearly scored on a 35-yard catch and run. At the time, it was Clemens’ longest pass play of the season — but that would change.

In any event, on this series Stacy took the handoff on the next play for a one-yard run and his fourth touchdown of the season.

The very next time the Rams touched the ball, they got seven more points. Austin fielded a Pat McAfee punt on the hop at the 2, headed for the right sideline and didn’t stop until he was in the opposite end zone 98 yards away. And this time . . . there were no flags.

Austin had an 84-yard punt return TD against Dallas and a 63-yard TD reception against Carolina wiped out by penalty earlier this season, but this one counted for the second-longest punt return in Rams history. Robert Bailey had a 103-yard punt return for a score in 1994, the last year for the Rams in southern California before moving to St. Louis.